The present invention relates to an electro-pneumatic positioner with a pneumatically driven dual-chamber actuator having a pneumatic main air intake valve and a pneumatic main air discharge valve attached to a pressure pipe leading to one actuator chamber. The positioner may also include a further pneumatic main air intake valve and a further pneumatic air discharge main valve attached to a further pressure pipe leading to a further actuator chamber. In addition, the positioner may include one actuating element for each main valve, with the actuating element for the one main air intake valve being formed by a control valve that acts upon a reversing valve of the one main air intake valve. The actuating element for the further main air intake valve being formed by a further control valve that acts upon a reversing valve of the further main air intake valve.
A conventional pneumatic positioner of this type Siemens SIPART PS 6DR3000 electro-pneumatic positioner, which is described in the Siemens operating instructions xe2x80x9cSIPART PS Elektro-pneumatischer Stellungsregler 6DR3000-1N/E bis 2N/Exe2x80x9d, SIPART PS Electro-Pneumatic Positioner 6DR3000-1N/E to 2N/E order number C73000-B7400-C136-1. As shown in FIG. 2 of the above-mentioned operating instructions, this conventional positioner has a control valve, designed as a piezoelectric valve, assigned to each main valve; a piezoelectric valve of this type is described in The Piezo Pill Curve, xe2x80x9cfluidxe2x80x9d, April 1989, pages 34 and 37. Two control valves, each interacting with the main valves on a pressure pipe of the dual-chamber actuator, are connected to a compressed air source via a pilot pressure regulator.
An object of the present invention is to simplify the design of the conventional electro-pneumatic positioner, while maintaining its advantageous technical characteristics, in order to reduce production costs.
To achieve this object, the actuating element of the one main air discharge valve of an electro-pneumatic positioner is formed, according to the present invention, by a feed pipe which connects the pressurized side of the one main air discharge valve to the interior of the reversing valve of the further main air intake valve; and the actuating element of the further main air discharge valve is formed by a further feed pipe which leads from the pressurized side of this main air discharge valve to the reversing valve of the one main air intake valve.
German Patent No. 195 37 493, describes an electro-pneumatic positioner that provides actuating elements in the form of feed pipes leading to two main valves, eliminating the need for two control valves. The actuating elements of the further main air intake valve and the further main air discharge valve in this positioner are formed by feed pipes.
One advantage of the positioner according to the present invention is that, compared to the conventional positioner described above, it is designed to eliminate the need for two control valves by having only feed pipes leading to the one pressure pipe and into the one reversing valve of the one main air intake valve instead of the two control valves for controlling the further main air intake valve and the further main air discharge valve. An additional advantage is that the use of only two control valves instead of the previous four control valves makes it possible to eliminate a pilot pressure regulator. According to an additional advantage, the reliability of the positioner according to the present invention is further increased over that of the known positioner because two control valves are replaced by fail-proof feed pipes.